Some school systems around the U.S. extended their holiday break Monday or switched back to online instruction because of the explosion in COVID-19 cases, while others pressed ahead with in-person classes amid a seemingly growing sense that Americans will have to learn to coexist with the virus.

Caught between pleas from teachers fearful of infection and parents who want their children in class, school districts in cities such as New York, Milwaukee, Chicago, Detroit and beyond found themselves in a difficult position midway through the academic year because of the super-contagious omicron variant.

New York City, home of the nation’s largest school system, reopened classrooms to roughly 1 million students with a stockpile of take-home COVID-19 test kits and plans to double the number of random tests done in schools.

“We are going to keep our schools open and ensure that our children are in a safe environment,” newly sworn-in Mayor Eric Adams said.

New Yorker Trisha White said that she feels the risk is the same for her 9-year-old son in or out of school and that being with classmates is far better for him than remote learning.

“He could get the virus outside of school,” she said as she dropped the boy off. “So what can you do? You know, I wouldn’t blame the school system. They’re trying their best.”

While the teachers union had asked the mayor to postpone in-person learning for a week, city officials have long said that mask requirements, testing and other safety measures mean that children are safe in school. The city also has a vaccination mandate for employees.

New cases of COVID-19 in the city shot up from a daily average of about 17,000 in the week before the holidays to nearly 37,000 last week.

Across the U.S., new COVID-19 cases have tripled in the past two weeks to over 400,000 a day, the highest level on record, amid a rush by many Americans to get tested.

The high infection rates and resulting worker shortages are putting a heavy burden on employers large and small. Thousands of airline flights have been canceled in recent days, and many businesses have shelved return-to-work plans.

Weekend garbage collection was delayed in New Orleans, and jury trials in several Colorado counties were suspended.

Some libraries on New York’s Long Island and a ski resort in New Hampshire had to close.

A restaurant owner in Atlanta has spent $700 on rapid test kits and resorted to testing workers in the parking lot to make sure he had enough help to staff a recent dinner shift.

Policymakers and health authorities have been mindful of the toll on the economy and the education system.

Public heath experts have said that eradicating the virus is unlikely and that the world will instead have to find a way to keep COVID-19 down to an acceptable level, the way it does with the flu.

Last week, after the Centers for Disease Control and Prevention cut the recommended COVID-19 isolation period from 10 days to five, CDC Director Dr. Rochelle Walensky said: “We want to make sure there is a mechanism by which we can safely continue to keep society functioning while following the science.”

In another development Monday that could have a bearing on the ability of schools to stay open, the Food and Drug Administration gave its OK for Pfizer booster shots for children as young as 12. Boosters already are recommended for everyone 16 and older.

Elsewhere around the country, the Los Angeles Unified School District announced Monday that schools will now reopen Jan. 11 because of omicron’s rise. Furthermore, the district’s 600,000 students and roughly 73,000 employees will have to show a negative COVID-19 test result to enter campus. The district will have a testing site as well as take-home test kits available.

In Wisconsin, the 75,000-student Milwaukee school system is going back to virtual instruction Tuesday because of rising cases among staff members. The district said it is aiming to return to in-person classes Jan. 10.

The Peoria, Illinois, district extended winter break by a week.

Schools in Davenport, Iowa, surprised parents early Monday by announcing the cancellation of all classes for the day because of a shortage of bus drivers that was blamed at least in part on COVID-19.

The president of the National Parents Union, a network of parent organizations, called the sudden switch back to virtual learning “an abomination.”

“Once again, parents are left scrambling at the last minute and, worse, far too many children are being deprived of an in-person learning experience, which is critical for their academic and social-emotional development,” Keri Rodrigues said in a statement.